Odds of Finding Alien Life Boosted by Billions of Habitable Worlds

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A new estimate of the number of habitable planets orbiting the
most common type of stars in our galaxy could have huge
consequences for the search for life.

According to a recent study, tens of billions of
planets around red dwarfs are likely capable of containing
liquid water, dramatically increasing the potential to find signs
of life somewhere other than Earth.

Red dwarfs are stars that are fainter, cooler and less massive
than the sun. These stars, which typically also live longer than
Class G stars like the sun, are thought to make up about 80
percent of the stars in the Milky Way, astronomers have said.

A second look

Red dwarfs generally have not been considered viable candidates
for hosting habitable planets. Since red dwarfs are small and
dim, the habitable zone surrounding them — the region where an
orbiting planet's surface water can remain liquid — is relatively
close to them.

"The habitable zone would be very, very small. Consequently, the
chances that you would actually find any planet at the right
distance from the sun to be attractive to life was likely to be
small, too," said Seth Shostak, a senior astronomer at the Search
for Extraterrestrial Intelligence Institute in Mountain View,
Calif. [ The
Strangest Alien Planets ]

But the study, based on data from the European Space Agency's
HARPS spectrograph in Chile, used a sample of 102 red dwarfs to
estimate that 41 percent of the dim stars might be hiding planets
in their habitable zone.

"The number of habitats might increase by a factor of 8 or 10,"
Shostak told SPACE.com.

Difficult environments

One of the largest concerns about planets circling red dwarfs is
radiation. A red dwarf's habitable zone is generally closer to it
than Mercury is to our sun, so a planet there would receive a
strong shock of particles when storms erupted on the red dwarf.

"They could essentially give everything on the surface that's
exposed to the sky ... a heavy dose of radiation," Shostak said.
"It could be fatal."

However, if the alien planet had a magnetic field, this could
provide some protection. So, too, could an ocean of water.
Life
that evolved beneath an ocean might be shielded from the
brunt of the radiation.

(That's not necessarily good news for SETI, which searches for
signals from extraterrestrial life. "We're not sure intelligent
life, if under water, will be building radio transmitters and
we're going to hear from them," Shostak said. "But it's
possible.")

Another problem with planets tightly bound to their host star is
a phenomenon known as
tidal locking, in which one side of the world is perpetually
turned toward the sun and receiving almost all of the heat.

But this isn't considered as big of a problem now as it had been.

For one thing, research over the past few years has indicated
that the presence of other planets can ease the grip of the
parent star, keeping a planet from being perfectly stagnant.

Furthermore, if the planet has an atmosphere, it might also boast
wind, which could move the hot atmosphere to the dark side and
the cool atmosphere to the sunlit side.

"Clearly, if it's too cold on one side and too hot on the other,
somewhere in the middle there's that lovely Goldilocks zone where
everybody wants to build their condos," Shostak said.

Even with these challenges, the sheer influx of tens of billions
of potentially habitable planets improves the chances of
finding alien life.

"SETI is looking for Mr. Right or maybe Ms. Right, depending on
your point of view," Shostak said. "It helps to find out that
there's 10 times as many candidates as there were before."

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